There is known an image forming apparatus capable of forming an image with a decoloring toner. A user uses a decoloring apparatus to decolorize an image formed on a sheet as it becomes unnecessary after confidential information is printed on the sheet with the decoloring toner. The user collects all the sheets on which the confidential information is printed to reduce the possibility of unwanted disclosure of the confidential information. However, as the sheet is managed manually, there is a case in which all the sheets on which the confidential information is printed cannot be reliably collected.